There are a lot of SCR turn-off methods but the SCR turn-off method of this invention is quite different from the conventional ones. Consider the SCR serving as a D.C. switch for example: When a turn-on voltage, is applied to the SCR gate, the SCR is caused to turn-on and the circuit of this invention works to keep the SCR on and to store electric energy for turn-off. When the turn-on voltage at the SCR gate is turned off, the circuit of this invention uses the stored electric energy to turn off the SCR. The turn-off action is so fast that it almost takes place at the same time as the turn-off signal, and no sparks occur. So it is very safe. When the pulse circuit works to send a positive pulse to the SCR gate, the SCR is turned on and the circuit of this invention works to keep the SCR on and to store electric energy for turn-off. When the voltage of the pulse at the SCR gate is zero, the SCR, with stored electric energy, is changed to its turn-off state. From the above, it is seen that by making use of the transient change of voltage at the gate, this invention makes the SCR change to its turn-off state and attains the objective to turn off the source current.